That doesn't neccesarily mean that they know what it CAN do- take the internet, for example. It basically started as a file-sharing system accross different computers. Who would've thought that it could handle real-time data exchange at high volumes for multiplayer games? In fact, it handled so well that only now are we saying "hey, it needs to be upgraded!'"
Eh... no. Little off there in your internet history, plus the developers knew what the internet could do. The funny thing about things that you code, is that you have to tell them exactly what you want them to do. They cannot think for themselves.
I guess people hear "new engine" and they think "from scratch", but that isn't necessarily so. A lot of functions, libraries, APIs, etc., are already written.